As a concise and direct answer to your question, here is a quote from Twain's essay "Concerning the Jews":
"I have no race prejudices, and I think I have no color prejudices or
caste prejudices nor creed prejudices. Indeed I know it. I can stand
any society. All that I care to know is that a man is a human
being--that is enough for me; he can'...
It's set in Louisiana because the town is based on a real town as she mentions in an NPR interview:
I got the idea for the book from a conversation I had with my mother,
who told me very offhandedly one day about a town she remembered from
her Louisiana childhood, where everyone sort of intermarried so that
their children would get lighter with each ...